Fuel cells may be classified as polymer electrolyte membrane fuel cells (PEMFC), phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, alkaline aqueous solution fuel cells (AFCs), or the like, according to the type of electrolyte used. The operating temperature of a fuel cell and the materials of parts thereof vary depending on the electrolyte used.
PEMFCs have a low operating temperature, high efficiency, high current density, high power density, short starting time, and a rapid response speed in response to a load change, relative to other fuel cells.
PEMFCs may be classified into direct methanol fuel cells using methanol fuel and hydrogen fuel cells using hydrogen fuel. A PEMFC has a stack structure of a plurality of membrane-electrode assemblies (MEA), each including a fuel electrode (anode) and an air electrode (cathode) each having a catalyst layer disposed respectively on gas diffusion layers (GDLs) disposed on opposite sides of a polymer electrolyte membrane. A GDL may be obtained by coating a carbon substrate as a porous carbon membrane with a microporous layer (MPL) onto which a catalyst layer is disposed.
To improve performance of a PEMFC, smooth introduction of fuel such as hydrogen, and an oxidant such as pure oxygen or air into the anode and the cathode, respectively, so as to diffuse into the catalyst layer is needed for smooth oxidation/reduction reaction in the catalyst layer. In particular, diffusion efficiencies of fuel and oxygen into the catalyst layer rely on the discharge rate of water produced in the cathode, and thus an effective water discharge structure for discharging water out of the fuel cell is important for the fuel cell. That is, a structure allowing smooth introduction of fuel and oxidant into the anode and cathode, respectively, so as to diffuse into the catalyst layer and smooth discharging of byproducts such as water out of the electrode is important for a fuel cell. Water flooding in the cathode may be a cause of sudden performance deterioration of the MEA.
Korean Patent Publication No. 2007-0079423 discloses a technology of manufacturing a gas diffusion layer with a uniform pore distribution without a crack in a microporous layer to allow smooth and uniform supply of fuel and reaction gas into a catalyst layer in order to increase catalyst utilization efficiency.
However, microporous layers and gas diffusion layers including the same known so far are still not satisfactory in water discharge ability, thereby further improvement in this regard still being necessary. To improve performance of a fuel cell in a high current density condition, heavily dependent upon water discharge ability, there is a need to improve the water discharge abilities of the microporous layer and, thus, the gas diffusion layer.